Its hard to say how much the benzos are holding you back. If I saw your diet and was watching your progress, I would better be able to answer your qustion. So sorry, I dont mean to be vague. Sure they can have an impact, but really if that is what you need, then there is not much you can do. There are other meds that will not mess you up mentally and will allow you to still get lean. Buspar comes to mind. I have used it myself for anxiety. Its not going to knock you out like xanax but it does help.
If this is something you have to use, I would like suggest you adjust the diet and keep trying to be your best given your given circumstances. There will never be a perfect time to get into shape
If you or anyone else is interested in working 1 on 1, I offer nutritonal programing through the Next Level Nutrition page, here at Naps